CODEWITHSUNDEEP
iosavfoundationcore-imageglkit
SushiGrass Jacob
SushiGrass Jacob

Reputation: 19814

GLKView + CIImage with Alpha + AVFoundation = Trippy Mess

I'm using AVFoundation to capture information from the camera, passing it to CIFilter to replace darker pixels with pixels with an alpha level of 0 and displaying it on a GLKView.

The containing view controller is a GLKViewController but the meat of the program starts with the function:

-(void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
    @autoreleasepool {

        CVPixelBufferRef pixelBuffer = (CVPixelBufferRef)CMSampleBufferGetImageBuffer(sampleBuffer);

                CIImage *image = [CIImage imageWithCVPixelBuffer:pixelBuffer options:[NSDictionary dictionaryWithObject:(id)kCFNull forKey:kCIImageColorSpace]];


        image = [image imageByApplyingTransform:CGAffineTransformMakeRotation(-M_PI/2.0)];

        CGPoint origin = [image extent].origin;
        image = [image imageByApplyingTransform:CGAffineTransformMakeTranslation(-origin.x, -origin.y)];

        [self.replaceDarkColorWithTransparentFilter setValue:image forKey:@"inputImage"];

        image = self.replaceDarkColorWithTransparentFilter.outputImage;

        [self.ciContext drawImage:image inRect:CGRectMake(0.0f, 0.0f, 480.0f, 640.0f) fromRect:[image extent]];
        [self.eaglContext presentRenderbuffer:GL_RENDERBUFFER];

        [self.replaceDarkColorWithTransparentFilter setValue:nil forKey:@"inputImage"];
    }
}

In the GLKViewController, I initialize the render buffer using:

glGenRenderbuffers(1, &_renderBuffer);
glBindRenderbuffer(GL_RENDERBUFFER, _renderBuffer);

The result is that older images are not being cleared and showing through. The result looks like this: http://d.pr/i/M02z Is this normal? Shouldn't it be clearing out the old context and starting fresh?

I've tried glFlush(); at update and glkView:(GLKView *)view drawInRect:(CGRect)rect and trying to draw nil for the Image in the CIContext to no avail.

Is there something I'm missing?

Upvotes: 2

Views: 2231

Answers (1)

Brad Larson
Brad Larson

Reputation: 170319

You're going to need to clear out the previous contents of your framebuffer using code like

glClearColor(0.0, 0.0, 0.0, 0.0);
glClear(GL_COLOR_BUFFER_BIT);

at some point before you draw the new Core Image frame. This will set the contents and alpha channel of the framebuffer to 0.0 to give you a clean slate on which to draw your filtered image.

You might also need to set the current OpenGL ES context using something like 

[EAGLContext setCurrentContext:self.openGLESContext];

right before that, because I can't remember if Core Image will leave that set properly for whatever thread you're working on.

Upvotes: 1

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